rusty cabling

[#1]

I have BT engineer coming tomorrow to have a look at my broadband speed after I managed to get BT to send one out (at last)
When I first got FTTC at my house it was with Plusnet and received a solid 70mbps (bearing in mind the cabling external was brand new as it's a new build house)
Over time, my speed started to deteriorate from September after 4 months of getting the physical line installed my speed went from 70's to around 50's mbps.
However when I remove the capping of the cable when it comes out of the ground, the bare cables (a range of colours, red, blue, green orange etc...) has become all rusty and smells a bit of mold.  I'm pretty sure the capping has either let in water or hasn't been installed properly by the contractor, yes a contractor.
Is this BT's fault or mine? Would the rust be affecting my download speeds and uploads?
many thanks

[#2]

It sounds like water damage and I would imagine that the rusty cable would play a part yes, the engineer would most likely strip the cable of the rusty parts and reconnect, as to whos fault it is that wouldn't be yours, BTO are responsible for everything leading into the home and including the master socket, everything within the home after the master socket is yours. 

[#3]

Engineer came,  I mentioned about the water damage and didn't say anything about it.
He stripped some jelly crimps that were behind the master socket and said it has been fitted incorrectly and corrected it.
He is now sitting in his van just outside of my house looking on his laptop and phone, I wonder if he is sponging of my WiFi ?
The speed has only increased by 1mbps (not good enough) and the upload hasn't increased at all,
I wonder if I should approach him and get him back in the house and see why I'm not getting my advertised speeds of 65mbps.  Is it worth the hassle or not?

[#4]

Given that you are not a PlusNET customer, why are you asking here?  I would have thought this a question for the BT forums.

[#5]

As BT forums are like banging your head against the wall,
ask you to send a message to a mod and takes several weeks to get a decent reply

[#6]

That maybe but there is no one here that can really help you as it's not your ISP,  if you want it fixed you have no choice but to contact BT, that rusty cable will still need looking at so mention it to BT that the engineer ignored you when you told him of a obvious fault that will need fixing other wise your issue will never get fixed.